Apparatus for thermal cracking of hydrocarbons



June 29, 1965 sHUSUKE MINAMI 3,192,013

APPARATUS FOR THERMAL CRACKING OF HYDROCARBONS Filed Nov. 5, 1962 United States Patent O ice 3,192,018 APPARATUS FOR THERMAL CRACKING F HYDROCARBONS Shusuke Minami, Hiro-machi, Kure-shi, Hiroshima-lien, Japan, assignor to Kabushiki Kaisha Hitachi Seisakusho, Tokyo-t0, Japan, a joint-stock company of Japan Filed Nov. 5, 1962, S81. No. 235,372 Claims priority, application Japan, Nov. 8, 1961, 36/ 39,749 4 Claims. (Cl. 23-262) This invention relates to an apparatus for pyrolysis or thermal cracking of hydrocarbons to produce lower olefins.

It is well known that when gases of such hydrocarbons as methane, ethane, propane, and naphtha are heated to high temperatures, they undergo pyrolysis, whereby it is possible to obtain lower olefins such as acetylene, ethylene, and butadiene which are raw materials for the petroleum chemical industry.

As one type of apparatus for such thermal cracking, there is a type known as a moving or fluid layer type, wherein circulation, that is, movement, takes place between a reaction section where pyrolysis action occurs and a regeneration section where heat replenishment for the reaction is accomplished. Heretofore, such apparatuses wherein sand, carbon, pebbles, coke, and other materials are used as heating media and are circulated between regeneration sections, where they are heated by combustion gases, and reaction sections, where they are caused to flow counter to the flow of the hydrocarbon and to undergo cracking reaction, have been proposed.

Such an arrangement as above-mentioned, in comparison with others wherein the combustion gas and the hydrocarbon are brought together with a tube wall interposed therebetween, has several advantages such as the possibility of lining the reaction tower inner wall with a refractory material, thereby increasing the heat resistance of the apparatus, the possibility of adjusting at will the contact time, the possibility of taking out the deposited carbon formed at the time of decomposition reaction together with the heating medium and removing this carbon, and the excellent transmission of heat in an apparatus of this type.

On the other hand, however, the heating media proposed heretofore, that is, such solid particles as sand, pebbles, and carbon particles, have a high rate of consumption of the particles themselves because of such destructive action during the moving process as wear due to mutual abrasion of the particles and wear due to collision and abrasion between the particles and the furnace wall and other wall structures. This wear causes the disadvantage of difiiculty in maintaining a suitable particle size and, moreover, creates the possibility of clogging of the circulation path by fine particles produced by these abrasive actions.

In view of the above considerations, the present invention seeks to achieve the following objects:

It is a principal object of the invention to provide an apparatus for pyrolysis of the present moving layer type wherein it is possible to maintain the heating medium at optimum particle size for the decomposition reaction, constantly throughout the operation of the apparatus.

It is another object of the invention to provide a pyrolysis apparatus wherein the consumption of the heating medium is low, regulation of the furnace interior temperature is easy, and the emciency of heat transfer is high.

pyrolysis apparatus as above-stated wherein heating of the heating medium can be easily accomplished.

The foregoing objects have been achieved by the present It is a further object of this invention to provide a 3,1992%13. Patented June 29, 1965 invention, which, briefly described, has the following unique features.

In the pyrolysis apparatus of this invention, a fusible metal of low melting point such as lead, tin, or a certain alloy is used as the heating medium and is caused, in the state of liquid droplets, to contact combustion gases in a regeneration chamber and to be thereby heated, giving up its sensible heat to the hydrocarbon in the reaction furnace. The heating medium to be introduced into the reaction furnace is pressurized and caused to pass through nozzles, the throat diameter of which is so determined as to create an injection pressure which will cause the liquid droplets injected into the reaction furnace to be of optimum size. The injected droplets are collected at the bottom of the reaction furnace and then conducted to the regeneration section.

For the sake of convenience, the reaction furnace is preferably so constructed that the heating medium is injected downwardly from the upper part of the furnace; Accordingly, it is necessary to transfer the heating medium collected at the bottom of the reaction furnace to the upper part of the furnace. It is desirablethat, during this transfer, the heating medium be heated by being caused to come in direct contact with combustion gases. For similar transfer of conventional heating media such as sand, pebbles, and carbon particles, the so-called gaslift, utilizing the combustion gases being used for heating as a carrying medium, is an effective means. In addition, such arrangements as those utilizing bucket elevators or those utilizing a separate air-lift have been used hitherto. Such conventional arrangements can be used with equal effectiveness also in the case of the apparatus, of the present invention wherein a molten fusible metal is used as the heating medium.

Thus, the pyrolysis apparatus according to this invention can be provided by simply converting portions of the arrangements of conventional pyrolysis apparatuses of moving layer type.

The details of this invention will be more clearly ap parent from the following detailed description of one representative embodiment thereof when taken in conjunction with the accompanying drawing, which is a schematic flow diagram showing the embodiment of the pyrolysis apparatus according to the invention.

Referring to the drawing, the apparatus comprises, essentially, a reaction section consisting of a pyrolysis furnace 1 in which pyrolytic reaction is accomplished and a regeneration section consisting of a combustion chamber 2 in which a fuel is burned to produce hot combustion gases, a heating chamber ,3 into which the said combustion gases are supplied from the bottom so as to heat the heating medium while, at the same time, conveying the said medium upwardly by gas-lift action, and a separator 4 which is so disposed as to receive the rising combustion gases and the heating medium from the heating chamber 3, and which is adapted to separate the gases and the heating medium and to accumulate and temporarily store the heated heating medium. The reaction and regeneration sections are connected by connecting pipes 5 and 6, which, together with the heating chamber 3, the. separator 4, and the pyrolysis furnace 1, form the circulation path for the heating medium.

The pyrolysis furnace 1 is provided at its upper part with a dispersing means 7. When the hot heating medium, which is a fusible metal in molten state, after passing through the connecting pipe 6, reaches the top of the furnace 1, it is injected in the form of liquid droplets by the dispersing means 7 into the furnace and, descending through the furnace interior, directly contacts and heats the hydrocarbon supplied separately into the furnace. This contact and heat exchange between the heating medium and the hydrocarbon may be accomplished by either counterflow or parallel flow, but in view of the rising force gained by the hydrocarbon upon being heated, a counterfiow operation, as adapted in the instant embodiment, is deemed to be more effective.

To the pyrolysis furnace 1 is connected a hydrocarbon supplying and decomposed gas extracting system comprising a preheater 8 for preheating the hydrocarbon to be processed, a decomposed gas cooler 9, and interconnecting pipes 10, 11, 12, and 13. The preheater 8 is in the form of a heat exchanger and is so adapted that the hydrocarbon to be processed, which is supplied thereto through the supply pipe 10, is preheated by heat exchange with the decomposed gas leaving the furnace 1 to a temperature which is suitable for pyrolysis of the hydrocarbon after it has entered the furnace.

The hydrocarbon gas leaving the preheater 8 through the pipe 11 is confluently joined, before it enters the furnace 1, by a flow of superheated steam supplied through a pipe 14, whereby the hydrocarbon gas is further heated to a state in which it can rapidly undergo the intended decomposition upon entering the furnace 1. For obtaining thermally cracked gas at a high yield rate, it is important that the heating temperature be constant and that the heating time be short. These conditions are fully satisfied by the preheating steps described above.

The hydrocarbon gas is decomposed in the furnace 1 by direct contact and heat exchange with the droplets of the heating medium, and the decomposed gas thus obtained is led out of the furnace by the pipe 12 to the preheater 8, where it gives up heat to the hydrocarbon gas to be processed, is then led to the cooler 9, where it is rapidly cooled so as to suppress secondary reactions which would otherwise follow.

The afore-mentioned combustion chamber 2 is supplied with fuel by a pipe 15 and with air for combustion by a pipe 16. The combustion chamber 2 is further supplied with recirculated combustion gas by a pipe 19 which is a part of a combustion gas recirculation (heat recovery) system comprising a pipe 17 which conducts out the combustion gas separated in the separator 4, a steam heater 20 to which the said combustion gas is conducted by the pipe 17, and in which a portion of the waste heat of the said gas is covered by steam, a pipe 18, a branch pipe 21 through which a portion of the combustion gas is discharged as waste gas from the circulation system, a blower 22 for pressurizing the remaining combustion gas, and the aforesaid pipe 19 for returning the pressurized combustion gas to the combustion chamber 2 so as to regulate the temperature within the heating chamber 3. The portion of heating chamber 3 directly adjoining combustion chamber 2, numbered 3a, is constricted for further regulation of the gas flow.

The steam heater 20, which is in the form of a heat exchanger, utilizes a portion of the heat of the combustion gas to heat steam which is then supplied through the aforementioned pipe 14 to join the flow path of the hydrocarbon gas as described hereinbefore. Thus, a portion of the heat of the waste gas from the regeneration section is recovered and supplied to the flow path of the gas to be processed.

By the use of the apparatus of this invention of the above-described construction, the process of pyrolysis of hydrocarbons can be accomplished with high efficiency.

Although this invention has been described with respect to a particular embodiment thereof, it is not to be so limited as changes and modifications may be made there- .in which are within the full intended scope of the invention, as defined by the appended claims.

What is claimed is: 1. A device for the pyrolysis of hydrocarbons comprising, in combination, a vertical reaction furnace; an inlet for hydrocarbons near the lower end of said furnace; an outlet for pyrolyzed hydrocarbons near the upper end of said furnace; heat exchange means connected to said inlet and said outlet; a separator for molten metal connected to the top of said furnace and provided with means to disperse said metal into fine particles; a return pipe for said molten metal at the bottom of said furnace; a heating chamber for said metal connected to said return pipe and to said separator; a combustion chamber disposed below said heating chamber and connected thereto; an air supply for said combustion chamber; supply means for fuel to be burned into combustion gases in said combustion chamber, said gases escaping into and through said heating chamber and into said separator, carrying with them said molten metal from said furnace back into said sepaartor by gas lift while reheating it; outlet means for said combustion gases from said separator; a superheated steam supply pipe connected to said hydrocarbon inlet, said steam carrying said hydrocarbons into said furnace without any mechanical pressure means; said finely dispersed molten metal countercurrently contacting said hydrocarbons in said furnace thus effecting pyrolysis.

2. The device as defined in claim 1 comprising, in addition, recirculating means for said combustion gases leaving said separator into said combustion chamber; second heat exchange means connected to said recirculating means and said superheated steam supply; and a drain for removal of part of the recirculated combustion gases, prior to reentry into said combustion chamber.

3. The device as defined in claim 1 comprising, in addition, a constriction in said heating chamber directly adjoining said combustion chamber for regulation of the flow of said combustion gases.

4. A device for the pyrolysis of hydrocarbons comprising, in combination, a vertical reaction furnace; an inlet for hydrocarbons near the lower end of said furnace; an outlet for pyrolized hydrocarbons near the upper end of said furnace; heat exchange means connected to said inlet and said outlet; a separator for molten metal connected to the top of said furnace and provided, within said furnace, with means for dispersing said metal into fine particles; a return pipe for said molten metal at the bottom of said furnace; a heating chamber for said metal connected to said return pipe and to said separator; a combustion chamber disposed below said heating chamber and connected thereto, said heating chamber being constricted at the juncture with said combustion chamher; an air supply and a fuel supply line for said combustion chamber, said fuel and air being burned therein to combustion gases, said combustion gases escaping through said heating chamber into said separator, carrying with them said molten metal from said furnace back into said separator by gas lift while reheating it; an outlet for said combustion gases from said separator connected to said combustion chamber; a pump disposed therebetween for returning the combustion gases to said combustion chamber; a branch pipe disposed in said outlet before said pump for removal of part of said combustion gases; a superheated steam supply line connected to said hydrocarbon inlet, said steam carrying said hydrocarbons into said furnace without any mechanical pressure means; a second heat exchanger connected to said superheated steam line and to said combustion gas outlet between the separator and the branch pipe; said hydrocarbons being contacted countercurrently by the finely dispersed molten metal particles in said furnace and thus being pyrolyzed.

References Cited by the Examiner UNITED STATES PATENTS 2,055,313 9/36 Ruthruff 196118 X 2,112,149 3/38 Edwards 196118 2,218,153 10/40 Pray 196-118 MORRIS O. WOLK, Primary Examiner.

JAMES H. HAY MAN, 111., Examiner. 

1. A DEVICE FOR THE PYROLYSIS OF HYDROCARBONS COMPRISING, IN COMBINATION, A VERTICAL REACTION FURNACE; AN INLET FOR HYDROCARBONS NEAR THE LOWER END OF SAID FURNANCE; AN OUTLET FOR PYROLYZED HYDROCARBONS NEAR THE UPPER END OF SAID FURNACE; HEAT EXCHANGE MEANS CONNECTED TO SAID INLET AND SAID OUTLET; A SEPARATOR FOR MOLTEN METAL CON NECTED TO THE TOP OF SAID FURNACE AND PROVIDED WITH MEANS TO DISPERSE SAID METAL INTO FINE PARTICLES; A RETURN PIP FOR SAID MOLTEN METAL AT THE BOTTOM OF SAID FURNACE; A HEATING CHAMBER FOR SAID METAL CONNECTED TO SAID RETURN PIPE AND TO SAID SEPARATOR; A COMBUSTION CHAMBER DISPOSED BELOW SAID HEATING CHAMBER AND CONNECTED THERETO; AN AIR SUPPLY FOR SAID COMBUSTION CHAMBER; SUPPLY MEANS FOR FUEL TO BE BURNED INTO COMBUSTION GASES IN SAID COMBUSTION CHAMBER, SAID GASES ESCAPING INTO AND THROUGH SAID HEATING CHAMBER AND INTO SAID SEPARATOR, CARRYING WITH THEM SAID MOLTEN METAL FROM SAID FURNACE BACK INTO SAID SEPAARTOR BY GAS LIFT WHILE REHEATING IT; OUTLET MEANS FOR SAID COMBUSTION GASES FROM SAID SEPARATOR; A SUPERHEATED STEAM SUPPLY PIPE CONNECTED TO SAID HYDROCARBON INLET, SAID STEAM CARRYING SAID HYDROCARBONS INTO SAID FURNACE WITHOUT ANY MECHANICAL PRESSURE MEANS; SAID FINELY DISPERSED MOLTEN METAL COUNTERCURRENTLY CONTACTING SAID HYDROCARBONS IN SAID FURNACE THUS EFFECTING PYROLYSIS. 